An ingrown nail (onychocryptosis) is also referred to as a “pincer nail”, and is a nail disease where a nail grows or cuts into one or both sides of the nail bed, thus causing a pain which may sometimes be very acute. As examples of causatives of the ingrown nail, there can be mentioned a pressure, an injury, a nail cut to the quick, and a congenital malformation. An ingrown nail is especially likely to occur at a first toenail. As conventional methods for curing the ingrown nail, there are known a method in which the ingrown portion of a nail is surgically removed (hereinafter, frequently referred to as a “surgical removal method”), a method in which a correcting device or a correcting apparatus is used, and a method in which a correction reagent is used. With respect to the methods using a correcting device or apparatus, reference can be made, for example, to U.S. Pat. No. 4,057,055 (Patent Document 1), and Unexamined Japanese Patent Application Laid-Open Specification Nos. Hei 8-215227 (Patent Document 2) and 2001-276104 (Patent Document 3). Further, with respect to the method using a correction reagent, reference can be made to Unexamined Japanese Patent Application Laid-Open Specification No. 2004-238288 (Patent Document 4).
However, the surgical removal method is disadvantageous in that this method is complicated and cumbersome, and the nail plate is permanently narrowed. Further, the surgical removal method has a problem in that, since a part of a nail which has grown or cut into the nail bed is cut away, the operation is difficult in the case where there is a danger of microbial infection. Furthermore, even in the case of the surgical removal method in which a part of the nail is removed to cure the ingrown nail temporarily, a relapse of the ingrown nail often occurs because the nail after the surgery still has an anomalous curvature such that the nail grows again into the nail bed. Therefore, it has been desired to develop a method for correcting an ingrown nail without surgery, i.e., without surgically removing the ingrown portion of the nail.
With respect to the method using a correcting device or apparatus, explanations are made below. For example, Patent Document 1 proposes an apparatus comprising: post members to be secured to lateral side portions of the external surface of a toenail; and a tension member, such as a rubber band, wherein each of the post members has an upstanding portion used for holding the tension member, and wherein the apparatus is so designed that the post members secured to the lateral side portions of the external surface of the toenail are drawn to each other by the tension member to thereby lift the lateral side portions of the nail. Patent Document 2 proposes a method in which a plate made of a shape memory metal or a resin is bent into a curvature and fittedly adhered to the curved surface of the ingrown nail by an adhesive, followed by elevating the temperature to a predetermined level or higher to thereby effect flattening of the plate, so as to correct the ingrown nail by the restoring force exerted by the plate made of a shape memory metal or a resin. Further, Patent Document 3 discloses an apparatus for correcting a deformed nail, and a method for correcting a deformed nail using the apparatus. More specifically, the apparatus disclosed in Patent Document 3 comprises wires each having a hooked end portion for holding a lateral side portion of an ingrown nail. In use of this apparatus, the lateral side portions of an ingrown nail are held by the respective hooked end portions of the wires, and the lateral side portions of an ingrown nail are laterally pulled toward the center of the nail by the hooked end portions of the wires. More specifically, the apparatus of Patent Document 3 comprises: a first correcting body comprising a first engaging portion to be engaged with a lateral side portion of a nail, a first contacting portion to be contacted with a part of the surface of a nail, and a first connecting hook portion, wherein the first contacting portion extends between and connects to each other the first engaging portion and the first connecting hook portion; a second correcting body comprising a second engaging portion to be engaged with the other lateral side portion of a nail, a second contacting portion to be contacted with a part of the surface of a nail, and a second connecting hook portion, wherein the second connecting portion extends between and connects to each other the second engaging portion and the second connecting hook portion; and a correcting operation portion which is engaged with both of the first connecting hook portion and the second connecting hook portion so that the first engaging portion and said second engaging portion are kept to be laterally pulled toward the center of the nail with a predetermined pulling force, thereby pulling upward the lateral side portions of the nail.
However, with respect to the apparatus described in Patent Document 1, it is difficult to satisfactorily correct an ingrown nail for the following reason. In the nail correcting operation using this apparatus, the force sustained by the lateral side portions of the nail is larger in the lateral direction toward the center of the nail than in an upward direction. Therefore, it is difficult to obtain a satisfactory correcting effect. Further, the correction of an ingrown nail by using this apparatus takes a very long time extending over a few or several months. Since each of the post members of this apparatus has an upstanding portion, which renders this apparatus bulky, an ingrown nail patient who has this apparatus fitted thereon is forced to live a very cumbersome and inconvenient life for such a long period of time. Thus, the apparatus described in Patent Document 1 is impractical. The method described in Patent Document 2 has the following problem. In this method, a plate made of a shape memory metal or a resin is bent into a curvature and fittedly adhered to the curved surface of the ingrown nail by an adhesive, followed by effecting flattening of the curved plate. In such case, the nail surface cannot follow the flattening of the plate, resulting in either that the plate is likely to come off from the nail surface (when the adhesion strength is low) or that the flattening of the curved plate is likely to be prevented (when the adhesion strength is high). In addition, the ingrown nail correction using this method takes a very long time extending over a few or several months, throughout which the correcting device remains fitted on the nail of the patient. Thus, this method is very cumbersome and inconvenient to the patient.
Also in the case of the method described in Patent Document 3, the ingrown nail correction takes a very long time extending over a few or several months, throughout which the correcting device remains fitted on the nail of the patient, as in the case of the method described in Patent Document 2. Thus, this method is also very cumbersome and inconvenient to the patient. This method has another problem in that, since the lateral side portions of an ingrown nail are held and pulled by the respective hooked end portions of the wires, pain and/or bleeding frequently occurs, thus increasing the burden on the patient. In addition, this method has a defect in that this method cannot be applied when the nail to be corrected is too hard or too fragile or has tinea unguium.
The method (using a correction reagent) described in Patent Document 4 is as follows. Patent Document 4 discloses a correction reagent for correcting a deformed nail, comprising at least one reducing agent selected from the group consisting of cysteine, thioglycolic acid and thioglycolate. The invention of Patent Document 4 is based on the application of permanent waving technology for hair to the correction of a deformed nail, wherein the application was conceived in view of the fact that the composition of a nail is similar to that of hair. More specifically, the method of Patent Document 4 is performed as follows. An emulsifier is added to the above-mentioned reducing agent (which is a main component of a first agent for use in permanent waving) so as to obtain a cream-like agent having a reducing agent content of 5% by weight. This cream-like agent is used as an agent for correcting a deformed nail. First, a deformed nail (such as an ingrown nail) is allowed to grow forward until it has a forward free end portion (not in contact with the nail bed) having a satisfactory length in the forward direction. Next, a few through-apertures are formed in the forward free end portion of the nail. Then, the above-obtained cream-like agent is applied to the entire outer surface of the nail and allowed to stand for about 30 minutes. By this treatment, the disulfide bonds of the keratin protein of the nail are cleaved to form two mercapto groups per disulfide bond, thereby softening the nail. After the treatment, the cream-like agent is washed away with warm water. The thus softened deformed nail is manually corrected into an appropriate shape. A cold-setting resin is applied to the outer surface of the resultant corrected nail so as to fill the apertures formed in the forward free end portion of the nail, thereby fixing the shape of the corrected nail, and the thus treated nail is allowed to stand for 1 hour. Thereafter, the cold-setting resin is removed from the nail. The correction method described hereinabove has defects in that, since the operation is performed manually, the method is cumbersome and needs a high skill. Also, this correction method poses the following problem. In this method, the deformed nail has to be fully grown so as to provide a forward free end portion having a length sufficient for the above-described resin fixation operation after the manual correction of the nail. However, in many or most cases, an ingrown nail patient has an ingrown nail cut to the quick; therefore, the correction of the ingrown nail cannot be performed until the ingrown nail has fully grown. Thus, this correction method is disadvantageous in that very frequently, this correction method cannot be performed immediately after an ingrown nail patient has decided to undergo a nail correction using this method.
It should be noted that the correction reagent used in the method described in Patent Document 4 cannot be used in combination with any of the conventional correcting devices or apparatuses (for example, the correcting devices or apparatuses disclosed in Patent Documents 1 to 3). The reason for this is as follows. The conventional correcting devices or apparatuses are premised on that they are used for correcting a nail in the ordinary state, that is, a stiff and hard nail (i.e., a non-softened nail). Therefore, if any of the conventional correcting devices or apparatuses are used on an ingrown nail in the softened state, the softened nail sustains too great a deforming stress (such as a buckling stress), so that the softened nail will suffer a drastic deformation, such as a drastic buckling. As a result, the desired correction of an ingrown nail cannot be attained at all. Especially, in the case where the correction reagent used in the method described in Patent Document 4 is used in combination with any of the correcting apparatus described in Patent Document 1 and the correcting device described in Patent Document 3, the force sustained by the lateral side portions of the nail is larger in the lateral direction toward the center of the nail than in an upward direction. Thus, it is very difficult for any of these correcting apparatus and correcting device to be used for correcting an ingrown nail in the softened state into a desired shape. Further, especially when the correcting device described in Patent Document 3 is used for correcting an ingrown nail in the softened state, the lateral pulling force (toward the center of the nail) is locally exerted only on the lateral side portions of the nail with which the hooked end portions of the wires are engaged, thus rendering it substantially impossible to correct the ingrown nail into a desired shape. Further, even when the correction reagent used in the method described in Patent Document 4 is actually used in combination with any of the conventional correcting devices or apparatuses despite the disadvantages caused by the correction reagent, the above-mentioned problems accompanying the use of the conventional correcting devices or apparatuses remain unsolved, and substantially the same problems occur. For example, even when the correction reagent used in the method described in Patent Document 4 is actually used in combination with the method described in Patent Document 2 (employing a plate made of a shape memory metal or resin), there occurs a problem in that the plate is likely to easily come off from the nail surface.    Patent Document 1: U.S. Pat. No. 4,057,055.    Patent Document 2: Unexamined Japanese Patent Application Laid-Open Specification No. Hei 8-215227.    Patent Document 3: Unexamined Japanese Patent Application Laid-Open Specification No. 2001-276104.    Patent Document 4: Unexamined Japanese Patent Application Laid-Open Specification No. 2004-238288.